This invention relates to a muscle implant designed for transplantation. The implant is both a functional and structural replacement for dysfunctional muscle tissue.
Muscle abnormalities are a fact of life whether they result from a developmental anomaly or from a traumatic injury or for any other reason. Structural defects to striated muscle tissue range from relatively functionally benign to profoundly debilitating disorders. In any circumstance, the condition can affect the patient on a number of different levels. For example, structural defects to the musculature of the face may have a minor impact on the ability of a patient to survive. However, even minor cosmetic defects of the muscle of the face can have substantial psychological implications.
In addition to the striated muscle abnormalities noted above, cardiovascular muscles are also subject to deterioration and disease. Congenital malformations of the heart are also common. Conventional surgical techniques are fundamentally unable to adequately restore the subtle structural and functional relationships that exist in a healthy heart. An intact heart has an elaborate three-dimensional structure that insures the orderly propagation of electrical signals and the coordinated contraction of the ventricular wall. If the heart muscle is to be effectively repaired, the three-dimensional organization must be addressed at the cellular level.
Very few alternative technologies exist for the reconstruction of dysfunctional skeletal muscle tissue. Attempts to fabricate such tissue have been generally confined to experiments in which skeletal muscle cells are trapped in a collagen gel. In these experiments, the cells have been seeded onto the exterior of a collagen gel or literally enveloped within the gel as it is polymerized. Subsequently, the cells are allowed to differentiate within the random, xe2x80x9cthree-dimensionalxe2x80x9d environment of the collagen gel. The distribution of cells within these collagen gels represents a limiting factor in these constructions. When muscle cells are seeded onto the exterior of a collagen gel they typically remain concentrated on the peripheral regions of the gel. Experiments in which muscle cells are directly incorporated into a collagen gel as it undergoes polymerization have yielded more densely and uniformly populated cultures; however, these constructions remain less dense than their in vivo counterparts. More importantly, the implants produced in conventional tissue culture are composed of muscle cells that lack a uniform alignment or orientation. The random nature of the cells within these sparsely populated implants limits the utility of that tissue and its ability to function as an ordinary muscle.
Additional constraints that must be addressed in designing an implant include the mechanical stability of the implant. The implant must have enough structural integrity to withstand manual manipulation, the surgical procedures and the mechanical environment of the intact tissue. Intact skeletal muscle is surrounded in vivo by multiple layers of a dense connective tissue that compartmentalizes the muscle and reinforces the structure of the tissue. Mimicking the specific structure of this arrangement in vitro is difficult, because any dense, investing material will tend to limit nutrient diffusion, oxygen transport and the removal of metabolic waste products away from the cells. Components made from artificial materials such as polyester mesh have been used with some success to increase the strength of the cultures while allowing them to retain a substantial portion of their elastic properties. However, the incorporation of synthetic materials into an implant can increase the likelihood that it will initiate an inflammatory response in vivo.
Cardiac tissue lacks a dense connective tissue. However, the muscle cell of the heart is organized into a complicated lattice. The individual muscle cells of the heart have a rod-like cell shape. Like skeletal muscle, they are oriented along a common axis in a complex three-dimensional pattern. Each cell of the heart is invested with a basement membrane and interconnected to its neighbors by a complex matrix of collagen fibrils. The three dimensional pattern of the cell layers within the heart is critical for the orderly propagation of electrical signals and the coordinate contraction of the ventricular wall.
Smooth muscle surrounds the supports of many of the hollow organs. For example, in the gut it surrounds the stomach and intestinal track. Contraction of this muscle mixes food and propels it along the digestive track. In the cardiovascular system smooth muscle cells surround the walls of the arteries and large veins and functions to control the caliber of the vessels. Smooth muscle lacks the nearly uniform cell shape and lattice like distribution of skeletal and cardiac muscle cells. However, smooth muscle cells do exhibit an elongated, bipolar cell shape. As a population they are organized along a similar axis in a series of overlapping cellular layers. This pattern of organization allows smooth muscle to exert contractile forces in a complex pattern.
Accordingly, it is an object of the present invention to overcome the foregoing drawbacks and to provide a muscle implant to a host in need thereof. The implant can be used in a variety of ways including to augment existing muscle, correct muscle deficiencies or as a functional and structural replacement for dysfunctional muscle tissue. Further, the invention includes a method for manufacturing the muscle implant.
In one embodiment, a muscle implant includes an extracellular matrix made of electrospun fibers and muscle cells disposed on the matrix. In another embodiment, the muscle implant comprises an extracellular matrix made of electrospun fibers for supporting muscle, a tendon made of extruded fibers, and a muscle cell layer that is disposed on the extracellular matrix. The muscle cell layer can be multilayered. In other variations, the electrospun fibers may be cross linked. Also, an oriented layer of collagen can be deposited onto the extracellular matrix so that the muscle cells are disposed onto the oriented layer of collagen.
In another embodiment, the invention includes an extracellular matrix for supporting muscle comprising a matrix of electrospun fibers. The fiber is discharged from an electrically charged orifice onto a grounded substrate to form the matrix. The matrix can also be treated with cross linking agents so that the fibers are cross linked.
The invention also includes a method of manufacturing an extracellular matrix comprising extruding electrically charged polymer solution onto a grounded target substrate under conditions effective to deposit polymer fibers on the substrate to form an extracellular matrix. The extruded polymer may form a three-dimensional matrix. The extracellular matrix may further include a gel of aligned collagen fibers deposited thereon.
In a further embodiment, the invention includes a method of forming a muscle fascial sheath by providing an electrically grounded substrate. There is further provided a reservoir of collagen solution wherein the reservoir has an orifice that allows the collagen solution to leave the reservoir. The collagen solution is electrically charged and then streamed onto the substrate to form a muscle fascial sheath.
In still a further embodiment, the invention includes a method of layering muscle cells on an extracellular matrix. The method includes providing an extracellular matrix and then placing the extracellular matrix inside a rotating wall bioreactor. A culture medium is loaded into the bioreactor wherein the medium comprises muscle cells. The bioreactor is then run until muscle cells attach to the extracellular matrix. Alternatively, the muscle cells attached to the extracellular matrix form multiple layers.